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How to To Demonstrate that the Boiling Point of a Liquid Depends on the Pressure

video How to To Demonstrate that the Boiling Point of a Liquid Depends on the Pressure

A light layer of vacuum grease is applied to the rim of the belljar. Water at room temperature is placed inside and the vacuum pump is then used to evacuate the vessel. When the air pressure is reduced to the vapour pressure of water at room temperature the water will begin to boil.

8 comments

Jul 3, 2009. 10:23 AMuberdum05 says:

I've had another theory about the pressure is lowered the water boils thing, that the water has oxygen in it, so that oxygen is being sucked out by the vacuum.

Feb 9, 2010. 8:19 AMEntropy512 says:

This is actually what happens if the pump pulls some vacuum but not enough to cause the water to boil. So a lot of people think they have caused water to boil but only removed dissolved gases.

However, if you have a good enough pump, you will eventually reduce the pressure to the point where water actually boils.

Brake bleeder hand pumps pull enough vacuum for the former, but not the latter.

It appears that the video was made using high end equipment capable of actually boiling water though.

Feb 4, 2010. 11:06 AMwupme says:

No its actually the oposite of a pressure cooker.
While the pressure cookier raises the boiling point with overpressur, the vakuum lowers it with underpressur.

What you see there ain't oxygen, it is realy water vaporizing because it reached its boiling point.
A nice proof of this is a restaurant i know in the Alps (Muechner Haus on the Zugspitze).
They have a lower air pressure because they are in about 3kilometers height. Because of that the kitchen HAS to use presure cooking technique to prepare food. Otherwise the water would boil at a way to low tempreature and food, like potatoes, would take ages to cook.

Feb 4, 2010. 12:14 PMuberdum05 says:

awesome.....